1. Technical Field
This invention relates to grain mixtures of steel and solid lubricant particles useful as a powder that is plasma sprayable and that readily transfers heat when deposited as a thin coating on surfaces exposed to high temperatures.
2. Discussion of the Prior Art
Automotive engines present a wide variety of interengaging components that generate friction as a result of interengagement. For example, sliding contact between pistons or piston rings with the cylinder bore walls, of an internal combustion engine, account for a significant portion of total engine friction. It is desirable to significantly reduce such friction by use of durable anti-friction coatings, particularly on the cylinder bore walls, to thereby improve engine efficiency and fuel economy, while allowing heat to be transmitted across such coatings to facilitate the operation of the engine cooling system.
Thick nickel plating on pistons and cylinder bore walls has been used for some time to provide corrosion resistance to iron substrates while offering only limited reduction of friction because of its softness and inadequate scuff resistance (see U.S. Pat. No. 991,404). Chromium or chromium oxide coatings have been selectively used in the 1980's to enhance wear resistance of engine surfaces, but such coatings fail to significantly reduce friction because of compatibility problems with piston rings as well as oil film formation problems and act more as a insulator. In the same time period, iron and molybdenum powders also have been jointly applied to aluminum cylinder bore walls in very thin films to promote abrasion resistance. Unfortunately, molybdenum particles and the many oxide forms of iron do not possess a low coefficient of friction that will allow for appreciable gains in engine efficiency and fuel economy.